West Nile Virus (WNV) is the most common arbovirus in the United States and causes yearly seasonal outbreaks. The spectrum of disease can range from an acute febrile illness to neuroinvasive diseases including meningitis, encephalitis and acute flaccid paralysis. Immunoglobulin M (IgM) detection in serum or cerebrospinal fluid (CSF) is the diagnostic method of choice for an acute WNV infection. Current practice in the utilization of diagnostic testing for WNV is unknown.
A retrospective multicenter study was conducted at 9 Memorial Hermann Hospitals in Houston, TX and it’s surrounding areas. We collected data on demographics, clinical presentations, laboratory results and outcomes in patients who presented with meningitis and a negative Gram stain between January 2005 and December 2009. WNV season was identified as patients presenting between May 1st to November 30th of each year.
A total of 721 pts (565 adult and 156 pediatric patients) were enrolled. WNV tests were sent in only 274 pts (38%). An onset during the WNV season (44% in WNV season vs. 32% in non-WNV-season), acute focal neurological deficit, Glasgow Coma Scale < 15, requirement of magnetic resonance image (MRI), empirical antiviral therapy, hospitalization and worse outcomes were significantly associated with utilization of WNV tests (p≤0.05).
Among 274 patients who were tested for WNV, 31 of them (12%) had laboratory results compatible with acute infection (10 pts with encephalitis and 21 pts with meningitis). Of those patients, 27 patients (87%) and 8 patients (26%) were diagnosed by positive serum and CSF IgM respectively. Five patients (16%) were sent for both tests which demonstrated concordant result results in 4 patients (80%) and one had positive serum but negative CSF IgM. Moreover, all patients with an acute WNV infection had onset of illness during the WNV season.
Testing for WNV is underutilized in clinical setting among patients presenting with meningitis and a negative Gram stain. Patients presenting with more severe disease are more commonly being tested raising the possibility of diagnostic bias in epidemiological studies. Serum IgM and/or CSF IgM for WNV are the standard test and should be sent only during the WNV season.
E. Aguilera, None
S. Wootton, None
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